Spark plug



.Oct. 28. '1924. 1,513,057

M. F. MACDCNALD SPARK PLUG Filed May 1, 1924 June" l'oz flayrzam' Ffifacdmz aid Patented Oct. 28, 1924.

UNITED STATES MAYNARD F. MACDONALD, OF VICTORIA, BRITISH COLUlVIBIA, GANADA, ASSIGNQR To HARRY n. MITCHELL, on SEATTLE, WASHINGTON.

SPARK PLUG.

Application filed May 1, 1924. Serial No. 710,408.

To all whom it may concern:

Be it known that I, MAYNARDLF. MAC- DONALD, a citizen of the United States, residing at 1449 Fort Street, Victoria, British Columbia, Canada, have invented certain new and useful Improvements Spark Plugs, of which the following'is a specification, reference being had therein to the accompanying drawings.

This invention relates to spark plugs for internal combustion engines and it has for its object to provide an improved deviceof this character constructed in such manner as to insure a hot spark at all times and to prevent the fouling of the plug by the accumulation of carbon deposits thereon. The means by which these objects are obtained are illustrated in the accompanying drawing, wherein Fig. 1 is a side elevation of a spark plug constructed in accordance with the invention;

Fig. 2 is a vertical sectional view therethrough;

Fig. 3 is an under side View; and

Fig. 4; is a horizontal sectional view upon line 44: of Fig. 1.

Like numerals designate corresponding parts in all of the figures of the drawing.

Referring to the drawing 5 designates the shell of the plug which is externally threaded at 6 to adapt it to be screwed into an engine cylinder and internally threaded at 7 for the reception of the packing gland 8. This packing gland serves a function common in devices of this character: viz; that of holding an insulating porcelain 9 in place by pressing a shoulder 10 of said porcelain against a shoulder 11 of the shell, suitable packing washers 13 and 14 being employed in a usual and well known way. At its lower end the shell 5 is provided with an apron 15 having a plurality of openings 16 formed in its side wall. The positive electrode consisting of a wire or rod 17 extends through the porcelain 9 in the usual way but this electrode differs from the electrodes ordinarily employed in that at its lower end it is provided with a ball 18 and the sparktakes place between the periphery of this ball and the rim or lower edge portion of the apron 15. The gap across which the spark jumps consists of the annular opening 20 between the periphery of the ball and the lower end portion of the apron 15. The ball is larger in diameter than the 16 areof considerable size, thus the com-- bined. area of these openings is materially in excess of the area of the spark gap formed by the annular opening 20. Consequently a free circulation of-the gases may be maintained through the spark gap. The passage of the gases through the annular space 20 keepsthis space'clean and free of carbon and thus prevents short circuiting of the plug. At the same time the presence of the openings 16 insures that such carbon and oil deposits as may be blown out of the annular space 20 will not find their way up into the body of the plug and accumulate there to constitute a source of trouble. The under sideof the ball presents a flaring surface and the upper edges of the openings 16 are outwardly flaring, as indicated at 16 This causes the current of air to travel, as before stated, in the direction indicated by the arrows in Fig. 2, and exerts such scouring action over the confronting faces of the ball and the inner edge of the rim of the apron as to maintain these parts bright and clean and in such condition as will insure the ready passage of the spark between them.

It is to be understoodthat the invention is not limited to the precise construction set forth but that it includes within its purview whateverchanges fairly come within either the terms or thezspirit of the appended claims.

Having described my invention, what I claim is: I

1. A spark plug comprising an externally threaded shell, a gland threaded 'into the upper end of said shell,-a porcelain held in place within the shell by said gland, an electrode carried by said porcelain comprising a rod passing therethrough and a ball upon the lower end of said rod, the lower end of the shell being provided with a depending apron. having openings formed through its sidewalls which openings lie above the center of the ball, that portion of the apron below said openings lying substantially opposite the center of the ball and the lower portion of the ball projecting materially below the 'lower edge of the apron, said openings having flaring upper edges which in conjunction with the flaring lower face of the ball direct the gases passing through the annular space between the ball and the lower edge of the apron, upwardly and outward-1y.

2.1L structure as recited in claim '1 wherein the lower end of the porcelain is provided with an opening, said ball being materially larger in diameter than the opening in the porcelain. V

3. A spark plug comprising an externally threaded shell, a porcelain supported therein, an electrode carried by said porcelain comprising a ball located at the lower nd of said porcelain, the lower end of the shell being provided with a depending apron having openings formed through its side walls, which openings lie above the center of the ball, that portion of the apron below said openings lying substantially opposite the center ofthe ball and the lower portion of the ball projecting materially below the lower edge of the apron, said opening having flaring upper edges which, in conjunction with the flaring lower face of the ball, direct the gases passing through the annular space between the ball and the lower edge of the apron, upwardly and out-' wardly.

4. A spark plug comprising a shell and a body of insulating material held therein, a positive electrode carried by said body of insulating material, a substantially straight side apron open at its bottom, substantially bottom of the shell may pass freely through the space between the said electrode and the lower inner edge of the apron and be discharged uniformly at all points in the circumference of the latter; 7

In testimony whereof I hereunto affix my signature.

MAYNARD F. MACDONALD. 

